This invention relates to a newly discovered phase of aluminum trihydroxide. This invention further relates to catalysts made from this new phase of aluminum trihydroxide, which catalysts may be specifically formulated to provide improved performance characteristics for a great number of hydrocarbon processing operations. This invention also relates to methods of producing this new phase of aluminum trihydroxide and catalysts made therefrom, and to a method of improving the activity of catalysts having a silica-alumina support.
The art relating to alumina-containing supports, impregnating such supports with various catalytically active metals, metal compounds and/or promoters, and various uses of such impregnated supports as catalysts, is extensive and relatively well developed. As a few of the many exemplary disclosures relating to these fields may be mentioned the following United States patents, all of which are incorporated herein by reference for all purposes as if fully set forth U.S. Pat. Nos. 2,838,444; 2,935,463; 2,973,329; 3,032,514; 3,058,907; 3,124,418; 3,152,865; 3,232,887; 3,287,280; 3,297,588; 3,328,122; 3,493,493; 3,623,837; 3,749,664; 3,778,365; 3,897,365; 3,909,453; 3,983,197; 4,090,874; 4,090,982; 4,154,812; 4,179,408; 4,255,282; 4,328,130; 4,357,263; 4,402,865; 4,444,905; 4,447,556; 4,460,707; 4,530,911; 4,588,706; 4,591,429; 4,595,672; 4,652,545; 4,673,664; 4,677,085; 4,732,886; 4,797,196; 4,861,746; 5,002,919; 5,186,818; 5,232,888; 5,246,569; 5,248,412 and 6,015,485.
While the prior art shows a continuous modification and refinement of such catalysts to improve their catalytic activity, and while in some cases highly desirable activities have actually been achieved, there is a continuing need in the industry for even higher activity catalysts, which are provided by the present invention.
Much of the effort to develop higher activity catalysts has been directed toward developing supports that enhance the catalytic activity of metals that have been deposited thereon. In an overwhelming majority of applications the material chosen for a support is alumina, most often xcex3-alumina, but silica-alumina composites, zeolites and various other inorganic oxides and composites thereof have been and are employed as support materials. In the case of alumina, various researchers have developed methods for preparing supports having various surface areas, pore volumes and pore size distributions that, when appropriate metals are applied, are particularly suited for catalyzing a desired reaction on a particular feedstock, whether that reaction be directed toward hydrodesulphurization, hydrodemetallation, hydrocracking, reforming, isomerization and the like.
In most cases, the xcex3-alumina supports are produced by activation (usually calcination) of pseudo-boehmite (AlOOH) starting material. On rare occasions, the support has been generated from one of the heretofore known aluminum trihydroxides (Al(OH)3), Gibbsite, Bayerite or Nordstrandite. When Bayerite or Nordstrandite is used as starting material, the resulting dehydrated alumina has a structure different from the more typical xcex3-alumina, often referred to as xcex7-alumina; for Gibbsite, the product alumina can be "khgr"-alumina. Each of these transitional aluminas possesses different textures (porosities and surface areas) from the more common xcex3-alumina. However, they generally suffer from lower thermal stability than xcex3-alumina; for a specific dehydration and calcination procedure, the loss of surface area for these aluminas is much greater than would be experienced by xcex3-alumina. U.S. Pat. No. 6,015,485 teaches a way to enhance the texture of xcex3-alumina supported catalysts by the in-situ synthesis of a crystalline alumina on the xcex3-alumina base support. From that teaching, higher activity catalysts have been produced.
As an example of the need for higher activity catalysts may be mentioned the need for a higher activity first stage hydrocracking catalyst. In a typical hydrocracking process, higher molecular weight hydrocarbons are converted to lower molecular weight fractions in the presence of a hydrocracking catalyst which is normally a noble metal impregnated silica-alumina/zeolite. State-of-the-art hydrocracking catalysts possess a very high activity and are capable of cracking high volume throughputs. Such catalysts, however, are highly sensitive to contaminants such as sulfur, metals and nitrogen compounds, which consequently must be removed from the hydrocarbon stream prior to the cracking. This is accomplished in first stage hydrocracking processes such as hydrodenitrogenation, hydrodesulfurization and hydrodemetallation. Hydrotreating catalysts utilized in these processes are typically a combination Group VIB and Group VIII metal impregnated alumina substrate. State-of-the-art hydrotreating catalysts, however, are not sufficiently active to allow processing of the same high volume throughputs as can be processed by the hydrocracking catalysts. As such, the first stage hydrocracking processes form a bottleneck in the overall hydrocracking process, which must be compensated, for example, in the size of the hydrotreating unit relative to the hydrocracking unit.
In accordance with the present invention, there is provided, in one aspect, a newly discovered phase of aluminum trihydroxide that is produced by hot-aging formed and calcined silica-alumina support made from amorphous alumina-rich silica-alumina powder in an acidic, aqueous environment. This newly discovered aluminum trihydroxide phase, herein named xe2x80x9cKamenetsitexe2x80x9d, can be distinguished from the three previously known phases, Gibbsite, Bayerite and Nordstrandite, by X-ray Diffraction analysis. When subjected to drying and calcination, Kamenetsite forms a material that is texturally and structurally different from other supports. The catalysts made from this material exhibit exceptionally high catalytic activity in many hydrotreating and non-hydrotreating reactions. Indeed, by appropriate adjustment of the aging conditions used in the production of Kamenetsite, the final texture of the catalyst can be tailored to a specific catalytic application. There is evidence that catalysts containing the same active metals and active metals loading perform differently with certain petroleum feedstocks depending upon the size and concentration of the crystalline alumina particles produced from different Kamenetsite-containing support precursors.
Also provided in this invention is a method of making Kamenetsite from amorphous alumina-rich silica-alumina powder. This method involves process steps that are similar to those taught in an earlier patent (U.S. Pat. No. 6,015,485). In the present invention, however, the starting material is different from that used in ""485 and the product of the process may be distinguished by the size and concentration of the crystalline alumina particles produced and in the performance of catalysts made from the support produced.
In another aspect, the present invention provides high activity catalysts comprising supports based upon Kamenetsite and impregnated with one or more metals from Group VIB and Group VIII of the Periodic Table.
In addition to the above catalyst, the present invention also provides a process for improving the activity of a catalyst composition comprising a particulate porous support comprising silica-alumina and amorphous alumina, and impregnated with one or more catalytically active metals, by the steps of:
(1) wetting the catalyst composition by contact with a chelating agent in a carrier liquid;
(2) aging the so-wetted substrate while wet;
(3) drying the so-aged substrate at a temperature and under conditions to substantially volatilize the carrier liquid; and
(4) calcining the so-dried substrate.
This process can readily be applied to existing catalysts comprising a particulate porous support containing silica-alumina and amorphous alumina, or can be utilized in a catalyst manufacture process concurrently with and/or subsequent to the impregnation of the support containing silica-alumina and amorphous alumina, with one or more catalytically active metals and/or compounds thereof. In addition, the process can be utilized to improve the activity of spent catalysts during regeneration, which spent catalysts comprise a particulate porous support containing silica-alumina and amorphous alumina, wherein the spent catalyst is wetted as in step (1) above subsequent to the removal of carbonaceous deposits therefrom, followed by steps (2), (3) and (4).
By performing these steps in the indicated order, it is believed (without wishing to be bound by any particular theory) that an interaction takes place between at least the silica-alumina, amorphous alumina, chelating agent and aqueous acid which, when subjected to the temperature and time conditions of the aging step, results in the appearance of Kamenetsite. Upon drying and calcining the product from this reaction a crystalline phase of alumina that may be distinguished from that produced in U.S. Pat. No. 6,015,485 by the size and concentration of the crystalline alumina particles produced. Crystallite size at the catalyst surface can be measured via well-known techniques involving transmission electron microscopy.
Concurrent with the appearance of this crystalline phase, an increase in the surface area of the catalyst is also achieved. In addition, in preferred embodiments, a structure is generated with a porosity peaking in a first region of pore size 40 xc3x85 or less, and more preferably in the range of 20 xc3x85 to 40 xc3x85, as measured by nitrogen porosimetry using the desorption isotherm.
The resulting high activity catalysts find use in a wide variety of fields as detailed in the many previously incorporated references. A particularly preferred use is as a first stage hydrocracking catalyst in hydrodenitrogenation, hydrodesulfurization and hydrodemetallation.
These and other features and advantages of the present invention will be more readily understood by those of ordinary skill in the art from a reading of the following detailed description.